1. Field of the Invention
The present invention relates to a process for the preparation of phosgene from chlorine and carbon monoxide, and, more especially, to the preparation of phosgene from chlorine and carbon monoxide by catalytic reaction therebetween in at least two stages.
2. Description of the Prior Art
Phosgene is a known, very important intermediate for a variety of chemical syntheses, especially in the chemistry of the polyurethanes, because it permits the manufacture of isocyanates from the corresponding amines.
The methods for the preparation of phosgene most frequently and typically employed consist of interreacting a mixture of chlorine and carbon monoxide. Such reaction can be carried out by the UV radiation or .gamma.-radiation, but industrially it is generally conducted in the vapor phase by passing a stream of chlorine and carbon monoxide over elemental carbon, for example, in the form of active charcoal.
Under these conditions, one of the principal problems presented by this method of manufacture is the removal of the heat evolved due to the great exothermicity of the reaction.
Conventional solutions to this type of problem typically consist of diluting the reaction gases either with a gas which is inert to the reaction or with tail gases from which the desired product has been removed. These two techniques each present additional disadvantages. In effect, the inert gas is lost, which increases the cost of the process, and the recycling of the tail gases requires the use of rotating machinery, the operation of which is always a delicate problem and hazardous when the products handled are as dangerous as carbon monoxide or phosgene.
In French patent application Ser. No. 75/01200, filed Jan. 8, 1975, assigned to the assignee hereof, there is described a process for the preparation of phosgene which consists of introducing the reactant chlorine in several stages. Undoubtedly this technique has permitted better control of the reaction, but the productivity of such facilities still is lacking.
And while consideration might be accorded the eventuality of introducing the carbon monoxide in a plurality of stages, the state of the art would appear to point in the opposite direction. In fact, as best as can be determined, the art is apparently unequivocal in its direction that the reaction should be carried out in the presence of an excess of carbon monoxide compare French Patent No. 2,109,186 or C.A., 74, 66,194 a!
Thus, there remains a need in the art for a simple and inexpensive, yet highly efficient procedure for the preparation of phosgene from chlorine and carbon monoxide gases.